Sedimentology and Characteristics of Miocene Shallow Marine Carbonate as Reservoir Alternative Based on Outcrop Analogue in Madura and Puteran Island, Northeast Java Basin

Abstract

Hydrocarbon exploration in Northeast Java Basin has Miocene Globigerinid Limestone – a deep-water facies – as one of its main reservoirs. New play concept is highly expected, especially in carbonate reservoir that involves facies varieties within a depositional system. Detailed sedimentology study was accomplished based on field stratigraphy measurement to suggest reservoir alternative and figure out the reservoir characteristic (porosity and permeability) by petrography and mercury intrusion porosimetry. Stratigraphy measurements show lateral facies distribution with inter-fingering contact of the exposed Miocene carbonates in Madura to Puteran Island. The facies variations are defined by grouping some facies into certain association with different characteristics. The first is coarsening upward sandy bioclastic floatstone with some paleo-soil interbeds (fringing reef facies, 7–22% moldic, intra-grain, vuggy, and fracture porosity). The facies contains quartz fragment from erosion of Ngrayong Fm. along with abundant macro-fossils and branching coral clasts. The second is massive coralline framestone – rudstone (carbonate build-up with 2–4% moldic porosity). It consists of 40–70 cm beds and made of massive corals and algae. Next is bioclastic wackestone – floatstone (lagoonal facies with 22–40% vuggy, channel, and inter-grain porosity and 4877 mD permeability). It is coarsening upward with some brachiopods and pelecypods. The last is foraminifer grainstone – rudstone (reefal limestone – fore reef facies with 22–28% vuggy, channel, and moldic porosity and 355 mD permeability) dominated by larger forams. Those characteristics of Miocene carbonates facies are generally controlled by dissolution process, but petrography analysis shows that depositional texture (product of depositional environment and mechanism) is the main influence. Grain supported foraminifer grainstone – rudstone facies acts as reservoir alternative in the area. Its good property is controlled by depositional environment with active current where this facies was formed (fore-reef that is directly influenced by oceanic current). The dominant composition of big foraminifers associated with red algae and some planktonic foraminifer indicate that study area has a more complex reef system than just deep-water facies, which caused only small composition of carbonate mud. This facies is more widely-distributed compared to the others, and interpreted to continue in the subsurface area.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015